Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $58.43   5.208%   $61.473   $61.47   $61.45   $61.50  
  Purchase #2 $78.88   6.732%   $84.1902   $84.19   $84.20   $84.20  
  Purchase #3 $212.49   6.158%   $225.5751   $225.58   $225.60   $225.60  
  Purchase #4 $27.33   5.196%   $28.7501   $28.75   $28.75   $28.80  
  Purchase #5 $196.64   12.767%   $221.745   $221.75   $221.75   $221.70  
  Purchase #6 $121.87   12.849%   $137.5291   $137.53   $137.55   $137.50  
  Purchase #7 $83.44   10.863%   $92.5041   $92.50   $92.50   $92.50  
  7 purchase totals = $779.08       $851.7666   $851.77   $851.80   $851.80